The present invention relates to an apparatus for mixing construction materials. More specificially, the present apparatus is constructed for preparing bituminous sludges or paste type mixtures such as bituminuous mixtures for installation in or on a surface such as a road surface, driveway surface or the like.
Mixers of this type are known in the art and comprise a mobile multiple chamber container which may be a vehicle for storing of mineral aggregate and the bituminuous binder agent. The container vehicle may be equipped with means for discharging predetermined, proportional quantities of the aggregate and binder agent into the mixer proper. The mixer may be connected to or may be arranged for cooperation with the vehicle. Such mixers are commonly intended for a continuous mixing operation and for continuously discharging of the mixed material onto the surface during travel or feed advance of the apparatus over the surface to be treated.
The mixer proper comprises two mixing tools each including a mixing shaft. The feed advance direction extends in a direction opposite to the direction of travel. The two mixing shafts rotate in opposite directions and are equipped with mixing blades which lift the material out of the center of the mixer to slope the material upwardly. The mixing tools, as they continue to rotate, transport the material in the direction toward the discharge opening or end of the mixer. Such discharge opening or end is located in the zone of the rear facing wall of the mixer.
In an apparatus of this type the circumferential speed of the mixing shafts, or rather of the mixing blades secured to these shafts, may be adjusted to a speed exceeding five meters per second (5 m/sec). The two mixing shafts have a given spacing from each other center to center. The enveloping circles defined by the rotating mixing blades secured to the mixing shafts have a diameter corresponding to about 1.5 times said given spacing between the mixing shafts. The radii of the trough sections correspond to about 0.75 times said given spacing. The width perpendicular to both said longitudinal axes corresponds to about 2.5 times said given spacing between the mixing shafts. The length of the mixing trough corresponds to about 2.4 times to 3.0 times the just mentioned width of the trough.
The relatively rapid drive of the mixer resulting in the above circumferential speed and the just mentioned dimensions of the mixer have been found to be basically useful. However, the required number of mixing blades is substantial because the mixing blades are spaced by 45.degree. from each other, whereby the blades are arranged in groups of four in such a manner that blades of one group reach into the zone of the blades of the next adjacent group of four blades. The blades, in addition to being arranged in groups of four, have trapezoidal shapes which widen radially outwardly. The blades are also adjustable in their angle of attack relative to the mixing shafts. The blades of one group are spaced from each other by 90.degree.. However, since the blades of one group reach into the zone of another group, the spacing between adjacent blades is 45.degree. as mentioned. Thus, a mixer of the just described type comprises at least nine groups of four blades each on each shaft which amounts to a total of 72 blades.
The above described features have the disadvantage that due to the large number of blades the weight of the mixer is correspondingly large. Further, the power required for driving such a mixer is also substantial due to said large number of blades and the resulting weight. Another drawback is seen in that the mixing space needs to be voluminous yet provides a poor accessibility when cleaning or repairs become necessary. In spite of the large number of blades the mixing intensity leaves room for improvement. This appears to be due to the fact that in spite of the large number of blades there remain large free spaces between the blades reaching into each other so to speak and these large free spaces in turn prevent the imparting of shearing forces to the materials to be mixed in the central zone of the mixer. Basically, in the just described apparatus merely two oppositely rotating mixing rollers are formed which are guided or rather arranged in parallel to each other and the interaction of which is rather limited in the central zone of the trough due to the highly liquid type characteristics of the material.